A conventional recognition system for a vehicle uses a radio detection and ranging device (radar), which recognizes the position of the other vehicle traveling a little away from a subject vehicle thereby to recognize the surrounding condition of the subject vehicle. Such a radar device is located on a straight road to radiate periodically a millimeter wave as a radar wave toward a predetermined range (for example, JP 2002-99986 A). This radar device receives a radar wave reflected by the other vehicle, and recognizes the other vehicle based on the result of reception of the reflected radar wave. Thus it becomes possible to predict possibility of collision between vehicles and carry out necessary processes to avoid such a collision.
However, the conventional system necessarily takes some time to collect sufficient number of pieces of position information with high reliability after the vehicle successfully acquired (captured) the other vehicle. If the surround condition, for example, positions of surrounding vehicles, is recognized with only a small number of pieces of position information, the recognition will likely become erroneous.
This is because the system will continuously receive noises, that is, radar waves reflected by an object, which need not be acquired, when the position of an object is acquired by using radar wave. It is therefore necessary to eliminate the noises. One approach is to use the position information of an object and output it only after the same object has been acquired a plurality of times. According to this approach, however, the information of a vehicle cannot be recognized, when the vehicle has just entered a range of capture of radar from outside such a range and has not been acquired sufficient number of times.